Surface phenomenological studies

The reason for this state of affairs may be seen in past emphasis on surface phenomenological studies which attempted to model the metal surface as an array of surface atoms with some valences saturated by subsurface metal atoms and other valences saturated by ions or molecules making up the environment. This model led to the description of the interface in terms of the Helmholz and Guy-Chapman double layer theories, and inhibitors were visualized as interfering with the double layer structure through adsorption on the surface atoms of the metal, thereby altering the electrochemical reaction rates which are governed by the energetics of the double layer. While this model has been... 

In his phenomenological study [1], Briick ordered a number of polymers in a row describing their affinity to become positively or negatively charged when rubbed with each other. Briick s row and other comparable rows first demonstrated the fundamental relationship between the chemical structure of a polymer and its tribo-electrical charging properties. In a former work [2] we followed that idea and showed that the tribo-electrical charging of two polymer species charged in a fluidized bed clearly depends on the affinity of the polymer surface to take up electron... 

The interface between a solid and its vapor (or an inert gas) is discussed in this chapter from an essentially phenomenological point of view. We are interested in surface energies and free energies and in how they may be measured or estimated theoretically. The study of solid surfaces at the molecular level, through the methods of spectroscopy and diffraction, is taken up in Chapter VIII. 

The importance of the solid-liquid interface in a host of applications has led to extensive study over the past 50 years. Certainly, the study of the solid-liquid interface is no easier than that of the solid-gas interface, and all the complexities noted in Section VIM are present. The surface structural and spectroscopic techniques presented in Chapter VIII are not generally applicable to liquids (note, however. Ref. 1). There is, perforce, some retreat to phenomenology, empirical rules, and semiempirical models. The central importance of the Young equation is evident even in its modification to treat surface heterogeneity or roughness. ... 

There is a large volume of contemporary literature dealing with the structure and chemical properties of species adsorbed at the solid-solution interface, making use of various spectroscopic and laser excitation techniques. Much of it is phenomenologically oriented and does not contribute in any clear way to the surface chemistry of the system included are many studies aimed at the eventual achievement of solar energy conversion. What follows here is a summary of a small fraction of this literature, consisting of references which are representative and which also yield some specific information about the adsorbed state. 

We now consider how one extracts quantitative infonnation about die surface or interface adsorbate coverage from such SHG data. In many circumstances, it is possible to adopt a purely phenomenological approach one calibrates the nonlinear response as a fiinction of surface coverage in a preliminary set of experiments and then makes use of this calibration in subsequent investigations. Such an approach may, for example, be appropriate for studies of adsorption kinetics where the interest lies in die temporal evolution of the surface adsorbate density N. ... 

The other class of phenomenological approaches subsumes the random surface theories (Sec. B). These reduce the system to a set of internal surfaces, supposedly filled with amphiphiles, which can be described by an effective interface Hamiltonian. The internal surfaces represent either bilayers or monolayers—bilayers in binary amphiphile—water mixtures, and monolayers in ternary mixtures, where the monolayers are assumed to separate oil domains from water domains. Random surface theories have been formulated on lattices and in the continuum. In the latter case, they are an interesting application of the membrane theories which are studied in many areas of physics, from general statistical field theory to elementary particle physics [26]. Random surface theories for amphiphilic systems have been used to calculate shapes and distributions of vesicles, and phase transitions [27-31]. 

In the process of establishing the kinetic scheme, the rate studies determine the effects of several possible variables, which may include the temperature, pressure, reactant concentrations, ionic strength, solvent, and surface effects. This part of the kinetic investigation constitutes the phenomenological description of the system. 

The interpretation of phenomenological electron-transfer kinetics in terms of fundamental models based on transition state theory [1,3-6,10] has been hindered by our primitive understanding of the interfacial structure and potential distribution across ITIES. The structure of ITIES was initially studied by electrochemical and thermodynamic analyses, and more recently by computer simulations and interfacial spectroscopy. Classical electrochemical analysis based on differential capacitance and surface tension measurements has been extensively discussed in the literature [11-18]. The picture that emerged from... 

The adsorption of organic molecules offers a rich phenomenology. A large number of studies have been performed on mercury electrodes, where the surface tension can be measured directly, and the surface charge and the capacity obtained by differentiation. We will not attempt to survey the literature, but consider a simple example the adsorption of aliphatic compounds. 

The effect of constraints introduced by confining diblock copolymers between two solid surfaces was examined by Lambooy et al. (1994) and Russell et al. (1995). They studied a symmetric PS-PMMA diblock sandwiched between a silicon substrate, and silicon oxide evaporated onto the top (homopolymer PMMA) surface. Neutron reflectivity showed that lamellae formed parallel to the solid interfaces with PMMA at both surfaces. The period of the confined multilayers deviated from the bulk period in a cyclic manner as a function of the confined film thickness, as illustrated in Fig. 2.60. First-order transitions were observed at t d0 = (n + j)d0, where t is the film thickness and d0 is the bulk lamellar period, between expanded states with n layers and states with (n + 1) layers where d was contracted. Finally, the deviation from the bulk lamellar spacing was found to decrease with increasing film thickness (Lambooy et al. 1994 Russell et al. 1995). These experimental results are complemented by the phenomenologi-... 

Recently, one of us (D. L. P.) has made [52] a detailed calculation for a cadmium interface which takes s- and p-like bands into full account. This is a very very nearly ab initio calculation of the molecular and electronic distributions at the interface of the (001) surface of hep cadmium and liquid water. In cadmium, unlike copper, the d electrons are not expected to make a significant contribution to the interaction of the electrode with the water, but because Cd is divalent, a study of Cd which includes nonlocality in the pseudopotential tests our ability to make a less phenomenological model in a system with more electrons per ion using these methods in a way that is computationally affordable. 

Several approaches may be used to develop better correlations of DMS and chlorophyll a. One approach is to extend surveys of laboratory cultured phytoplankton (24) to identify which organisms biosynthesize DMSP. However, until there is a better understanding of the underlying biochemistry of DMSP, these studies may be largely phenomenological. Another possibility is the empirical approach, where large extents of the surface oceans are sampled and DMS and chlorophyll a determined simultaneously (53). 

Following the above-outlined phenomenological considerations, scientists have studied various surfaces with respect to protein adsorption, and a number of different surface chemistries have been successfully applied to the design of surfaces that resist the adsorption of proteins. 

---